According to the BBC article the reason they picked these groups, students and spouses, was because they are "the most likely to foreign nationals who officials say are most at risk of abusing immigration rules - students and those on a marriage or civil partnership visa."
I can see students being violators; they probably have little to lose. They have no recourse to stay, but spouses? They have no reason to not follow the rules. They will be kicked out and not allowed to live their spouse.
I think they chose spouses because, unless they want to move to another country which could be difficult or impossible, they have no other recourse. A student could decide to go to school somewhere else, a worker could choose to get job in another place, but you and your spouse only have a limited number of options.